1. Field of the Invention
The present invention relates to a rotating electrical machine for a vehicle having a rotor with a permanent magnet for supplying magnetic flux to an armature core.
2. Description of the Related Art
In known vehicular alternators using a permanent magnet as a field magnet, there has been a technique that is capable of reducing the amount of electric power generation during the high speed rotation of an alternator so as to prevent the destruction thereof due to overvoltage to a battery or an electrical load. In such a technique, a permanent magnet magnetized in a direction to reduce leakage flux is interposed between the magnetic poles of a claw pole rotor, and the specification of this permanent magnet is adjusted in such a manner that the output of the alternator at a maximum rotational speed thereof when the field current of a field winding is made zero becomes a magnetic excitation force that is substantially equal to and does not exceed the demand value of the normal load of a vehicle (see, for example, a first patent document: Japanese patent No. 2674556 (pages 2 and 3, FIGS. 1 through 4)).
According to the vehicular alternator referred to above, however, there arises the following problem. That is, when the field current is made zero after excitation due to the field current is performed, the remanence remains in a field core, and In this case, even if the excitation force due to the permanent magnet is adjusted, the output of the alternator during the high speed rotation thereof is caused to increase under the action of the remanence, so the battery is brought into a state of overvoltage.